VFD Capacitor Reforming Guide

VFD Capacitor Reforming Guide


1. About Reforming Capacitors

Ensure that capacitors are reformed once a year when stored with the power off. If drives have been stored and non-operational for more than a year, capacitors may get damaged when operating the drive under load. When smoothing capacitors are stored under no load conditions for more than 1 year, its leakage current tends to increase.

When storing capacitors at a high temperature, the leakage current will increase considerably. This is due to a drop in the withstand voltage of the dielectric caused by the reaction of the anode oxide layer with the electrolyte. At this point the capacitor should not be subjected to full voltage until the leakage current returns to its initial level. This is accomplished by reforming the electrolyte.

Reforming can be done by applying a voltage that is slowly increased to the rated voltage over a period of several hours, with current limited to rated leakage current.

2. Reforming Recommendations

It is advisable to use a three-phase variable voltage source(slidacs or variacs) capable of producing 110% of the drive’s rated input voltage (220V/440V x 1.1 = 242/484Vrms). Use a three-phase or single-phase 50 / 60Hz variable transformer to supply power. Never connect the motor to the output terminals while reforming.  

3. Reforming Methods

(1) Connect a variable voltage source across the input.

(2) Slowly raise the voltage to 100 Vrms. Hold for 15 minutes

(3) Slowly raise the voltage in 100 Vrms increments, holding each for 15 minutes.

(4) Once you have raised the input voltage to the drives rated voltage, wait 15 minutes and then turn off the power.

(5) Leave the power supply for 1 hour after applying the rated voltage to supply energy to the drive.